246 



THE HEART. 



often cribriform or perforated with holes, is an important structm-e in 

 the fcEtal heart, and serves the purpose of directim;- the stream of blood 

 from the inferior cava through the foramen ovale into the left auricle. 

 The other openings into the right auricle are 1, — i\\Qcmriculo-ventricnlar 

 aperture, situate in front of the inferior vena cava and occupying the 

 anterior and under part of the cavity : it is oval in form and large, 

 admitting three fingers easily ; 2, the orifice of the large coronary vein of 

 the heart (fig. 1C7, 3"), situated between the inferior cava and the 

 auriculo-ventricnlar opening : this is guarded by a semicircular valve, 

 sometimes double, Avhich, although previously figured by Eustachius, is 

 often named valve of Thebesius ; 3, openimjs of one or two lesser 

 cardiac veins ivom. the surface of the right ventricle ; and 4, t\iQ fora- 

 mina of Thehesins, a number of small pits variously situated, some of 

 which are merely recesses closed at the bottom, whilst others are the 

 mouths of small veins {veme minimcG cordis). 



IGS. 



Fig. 168. — View of the Adult Heart, frox 



BEHIND, TO SHOW THE CuRONARY VeINS (Allen 



Tliomson). One-third the Natural Size. 



«, jilaced on the back of the right auricle, 

 points to the Eustachian valve seen ■within 

 the opening of the inferior vena cava ; b, left 

 auricle ; c, right ventricle ; d, left ventricle ; e, 

 vena cava superior ; /, arch of the aorta ; 

 1, coronaiy sinus ; 2, great coronary vein turn- 

 ing reund the heart in the anriculo- ventricular 

 groove ; 3, 4, iiosterior branches ; 5, one of the 

 small right cardiac veins passing directly into 

 the right auricle ; 6, the vestige of the left 

 superior vena cava i^roceeding over the left 

 auricle downwards to join the coronary siuns. 



The coronary vein (fig. 168, 1) is con- 

 siderably dilated before it enters the auricle, 

 and this dilated iiortion, -ndiich is imbedded 

 in the posterior "svall of the left aiuicle, is 

 tenned the " coronary sin us." At the junc- 

 tion of the coronary ""vein with the 

 dilated portion there is a valve con- 

 sisting of one or two segments. Other 

 small veins likewise enter the coronary sinus, each of them protected by a 

 valve. One of these small veins, the 'lobliav^e _. vein " of Marshall (fig. 168, 

 (5), takes a straight course from the vestigial fold before mentioned, over the 

 back of the left auricle, to open into the coronaiy sinus. This vein has no valve 

 over its orifice : it, together with the coronaiy sinus, is to be looked upon as the 

 remnant of the original lelt superior cava of the enibiyo (vide antea, p. 212). 



The right or anterior ventricle (fig. 165, 1) occupies the chief part 

 of the anterior surface of the heart, the right border, and a smaller 

 portion of the posterior surface. It extends nearly, but not quite, 

 to the apex. The. upper and left angle is prolonged in a conical 

 form to the commencement of the pulmonary artery : this part of 

 the ventricle is named conns arteriosus, or infundihulurn. The muscular 

 wall of this ventricle is thickest at the base, and becomes thinner 

 towards the apex. When tiie cavity is laid open (fig. IG7) the septum 

 of the heart is seen to bulge into it, so that the cross section is 

 crescentic in form (fig. 169). At the base of the ventricle are two 



